The Anteroposterior Positioning of Viscoelastic Cervical Disc Prosthesis Does Not Alter the Outcomes.

BACKGROUND: While first-generation articulated disc prostheses had an ideal positioning schematically as posterior as possible because of their geometrically determined center of rotation, the dogma may change for viscoelastic implants, whose center of rotation is free. Our hypothesis was to assess whether the anteroposterior positioning (APP) of a viscoelastic implant may influence the clinical or radiological outcomes at follow-up. METHODS: Twenty-five patients (mean age 47 years) were evaluated, with an average follow-up of 25.9 months. The primary outcome was the implants' APP on lateral radiographs. APP between 0% and 49% meant anterior centering, 50% perfect centering, and 51% to 100% posterior centering. The cohort was divided into 2 groups: anterior positioning and posterior positioning. Measurements were performed blindly to the functional outcomes. Visual analog scale for neck pain and radicular pain and the Neck Disability Index were assessed. Range of motion was measured at the last follow-up. The C2 to C7 Cobb angle and the spinocranial angle were also measured. RESULTS: The median crude offset from the vertebral endplate center was 0.4 mm (mean: 0.3 mm, Q1: -1.5 mm, Q3: 2 mm; range, -2.9 to 4 mm). The mean overall APP was 49%, 45.2% (95% CI, 43.2%-47.1%) in the anterior group, and 54.1% (95% CI, 51.4%-55.3%) in the posterior group. Fifteen patients were in the group anterior positioning and 10 in the group posterior positioning. The mean spinocranial angle was 79° preoperatively and 74° preoperatively (P = 0.04). Functional outcomes were significantly improved at the last follow-up (P < 10-4). There was no significant correlation between the APP, functional outcomes, and range of motion. CONCLUSION: The APP of the CP-ESP viscoelastic disc arthroplasty does not significantly influence the clinical or radiological outcomes at follow-up. This study suggests that this type of implant tolerates greater variability in its implantation technique.

Patient perception of leg length after total hip arthroplasty does not correlate with sagittal lumbar spine stiffness, history of spinal pathology or fusion.

PURPOSE: Although spinal pathology or fusion can change patients' posture and pelvic orientation, their correlation with perception of limb length discrepancy (LLD) after total hip arthroplasty (THA) is not well understood. We hypothesised that LLD perception after THA would not correlate with a history of spinal pathology, fusion or sagittal lumbar spine stiffness among patients who underwent THA. METHODS: Four hundred consecutive patients who underwent THA and had a complete set of anteroposterior and lateral EOS® imaging in standing and sitting positions were included in this retrospective case-control study. All patients underwent THA between 2011 and 2020. Sagittal lumbar spine stiffness was measured by changes in lumbar lordosis and sacral slope from the standing to the sitting position (lumbar spine stiffness: standing sacral slope-sitting sacral slope < 10°). Anatomical and functional lower extremity length, change in the centre of hip rotation, coronal and sagittal knee alignment, and hindfoot height were measured. Multiple logistic regression was used to investigate the correlation between patient perceptions of LLD, and the variables found to be significant in the univariate analysis. RESULTS: There was a substantial difference between the patients with and without LLD perceptions regarding axial pelvic rotation (p = 0.001), knee flexum-recurvatum (p = 0.007) and hindfoot height (p = 0.004). There was no significant difference between patients with and without LLD perceptions regarding differences in femoral length (p = 0.06), history of spine pathology or fusion (p = 0.128) and lumbar spine stiffness (p = 0.955). CONCLUSIONS: Our study found no significant correlation between perceptions of LLD after THA and spinal fusion or lumbar spine stiffness. Changes in the position of the centre of hip rotation can affect the functional leg length. Surgeons should consult patients regarding other factors, such as knee alignment or hind-/midfoot pathologies, as well as compensatory mechanisms, such as axial pelvic rotation, that could affect perceptions of LLD.

Small Random Angular Variations in Pelvic Tilt and Lower Extremity Can Cause Error in Static Image-based Preoperative Hip Arthroplasty Planning: A Computer Modeling Study.

BACKGROUND: Many THA simulation models rely on a limited set of preoperative static radiographs to replicate sagittal pelvic tilt during functional positions and to recommend an implant orientation that minimizes the risk of prosthetic impingement. However, possible random changes in pelvic or lower extremity angular motions and the effect of coronal and axial pelvic tilt are not included in these preoperative models. QUESTIONS/PURPOSES: (1) Can prosthetic impingement occur if the pelvic tilt or lower extremity alignment randomly varies up to ± 5° from what is measured on a single preoperative static radiographic image? (2) Do changes in coronal and axial pelvic tilt or lower extremity alignment angles have a similar effect on the risk of prosthetic impingement? METHODS: A de-identified pelvis and lower-body CT image of a male patient without previous THA or lower extremity surgery was used to import the pelvis, femur, and tibia into a verified MATLAB computer model. The motions of standing, pivoting, sitting, sit-to-stand, squatting, and bending forward were simulated. THA implant components included a full hemispherical acetabular cup without an elevated rim, polyethylene liner without an elevated rim, femoral head (diameter: 28 mm, 32 mm, 36 mm, or 40 mm), and a triple-taper cementless stem with three different neck shaft angles (127°, 132°, or 135°) with a trapezoidal neck were used in this model. A static model (cup anatomical abduction 40°, cup anatomical anteversion 20°, stem anatomical anteversion 10°) with a predefined range of sagittal pelvic tilt and hip alignment (0° coronal or axial tilt, without random ± 5° change) was used to simulate each motion. We then randomly varied pelvic tilt in three different pelvic planes and hip alignments (flexion, extension, abduction, adduction, rotation) up to ± 5° and assessed the same motions without changing the implant's anatomical orientation. Prosthetic impingement as the endpoint was defined as mechanical abutment between the prosthetic neck and polyethylene liner. Multiple logistic regression was used to investigate the effect of variation in pelvic tilt and hip alignment (predictors) on prosthetic impingement (primary outcome). RESULTS: The static-based model without the random variation did not result in any prosthetic impingement under any conditions. However, with up to ± 5° of random variation in the pelvic tilt and hip alignment angles, prosthetic impingement occurred in pivoting (18 possible combinations), sit-to-stand (106 possible combinations), and squatting (one possible combination) when a 28-mm or a 32-mm head was used. Variation in sagittal tilt (odds ratio 4.09 [95% CI 3.11 to 5.37]; p < 0.001), axial tilt (OR 3.87 [95% CI 2.96 to 5.07]; p < 0.001), and coronal tilt (OR 2.39 [95% CI 2.03 to 2.83]; p < 0.001) affected the risk of prosthetic impingement. Variation in hip flexion had a strong impact on the risk of prosthetic impingement (OR 4.11 [95% CI 3.38 to 4.99]; p < 0.001). CONCLUSION: The combined effect of 2° to 3° of change in multiple pelvic tilt or hip alignment angles relative to what is measured on a single static radiographic image can result in prosthetic impingement. Relying on a few preoperative static radiographic images to minimize the risk of prosthetic impingement, without including femoral implant orientation, axial and coronal pelvic tilt, and random angular variation in pelvis and lower extremity alignment, may not be adequate and may fail to predict prosthetic impingement-free ROM. CLINICAL RELEVANCE: Determining a safe zone for THA implant positioning with respect to impingement may require a dynamic computer simulation model to fully capture the range of possible impingement conditions. Future work should concentrate on devising simple and easily available methods for dynamic motion analysis instead of using a few static radiographs for preoperative planning.

How much change in pelvic sagittal tilt can result in hip dislocation due to prosthetic impingement? A computer simulation study.

Developing spinal pathologies and spinal fusion after total hip arthroplasty (THA) can result in increased pelvic retroversion (e.g., flat back deformity) or increased anterior pelvic tilt (caused by spinal stenosis, spinal fusion or other pathologies) while bending forward. This change in sagittal pelvic tilt (SPT) can result in prosthetic impingement and dislocation. Our aim was to determine the magnitude of SPT change that could lead to prosthetic impingement. We hypothesized that the magnitude of SPT change that could lead to THA dislocation is less than 10° and it varies for different hip motions. Hip motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting and pivoting in Matlab software. The implant orientations and SPT angle were modified by 1° increments. The risk of prosthetic impingement in pivoting caused by increased pelvic retroversion (reciever operating characteristic [ROC] threshold as low as 1-3°) is higher than the risk of prosthetic impingement with increased pelvic anteversion (ROC threshold as low as 16-18°). Larger femoral heads decrease the risk of prosthetic impingement (odds ratio {OR}: 0.08 [932 mm head]; OR: 0.01 [36 mm head]; OR: 0.002 [40 mm head]). Femoral stems with a higher neck-shaft angle decrease the prosthetic impingement due to SPT change in motions requiring hip flexion (OR: 1.16 [132° stem]; OR: 4.94 [135° stem]). Our results show that overall, the risk of prosthetic impingement due to SPT change is low. In particular, this risk is very low when a larger diameter head is used and femoral offset and length are recreated to prevent bone on bone impingement.

Sagittal Spinopelvic Translation Is Combined With Pelvic Tilt During the Standing to Sitting Position: Pelvic Incidence Is a Key Factor in Patients Who Underwent THA.

BACKGROUND: Sagittal spinopelvic translation (SSPT) is the horizontal distance from the hip center to the C7 plumb line (C7PL). SSPT is an important variable showing the overall patient balance in different functional positions which could affect the rate of hip instability. This study investigates the SSPT modification in patients who underwent total hip arthroplasty (THA). METHODS: A total of 120 patients were assessed preoperatively and postoperatively on standing and sitting acquisitions (primary unilateral THA without complication). SSPT is zero when the C7PL goes through the center of the femoral heads and positive when the C7PL is posterior to the hips' center (negative if anterior). Three subgroups were defined based on the pelvic incidence (PI): low PI <45°, 45°< normal PI <65°, or high PI >65°. RESULTS: The overall mean preoperative SSPT change from standing to sitting was 2.2 cm ([-7.2 to 17.4]) (P < .05). The overall mean postoperative SSPT change from standing to sitting was 1.2 cm ([-14.2 to 22.4]) (P < .05). In low- and normal-PI groups, standing to sitting SSPT and preoperative to postoperative changes in standing SSPT were increased significantly after surgery with the C7PL behind the hips' center (P < .05). In the high-PI group, standing to sitting SSPT was increased postoperatively (P = .034) (no significant changes from preoperative to postoperative status in standing and sitting). CONCLUSIONS: Adaptation from standing to sitting positions combines pelvic tilt and anteroposterior pelvic translation. THA implantation induces significant changes in SSPT mainly for low- and standard-PI patients. This is an important variable to consider when investigating the causes of THA subluxation or dislocation.

How do global sagittal alignment and posture change after total hip arthroplasty?

BACKGROUND: Postural change after total hip arthroplasty (THA) is still a matter of discussion. Previous studies have mainly concentrated on the pelvic motions. We report the post-operative changes of the global sagittal posture using pelvic, spinal, and lower extremities parameters. METHODS: 139 patients (primary THA, without previous spinal or lower extremity surgery) were included. We measured pelvic parameters [SS, sacral slope; PI, pelvic incidence; PT, pelvic tilt; APP angle, anterior pelvic plane angle] and the global posture parameters (SVA, sagittal vertical angle; GSA, global sagittal angle; TPA, T1 pelvic angle). Patients were categorized into low PI group < 45°, 45° < medium PI < 65°, and high PI > 65°. RESULTS: Mean GSA and SVA decreased post-operatively (p = 0.005 and p = 0.004 respectively). The TPA change was not significant (p = 0.078). In the low PI group, GSA (5.4 ± 5.0 to 4.3 ± 4.0, p = 0.005) and SVA (5.4 ± 4.9 to 4.2 ± 4.1, p = 0.038) decreased with more posterior pelvic tilt. Post-operative TPA was significantly higher (8.4 ± 10.6 to 9.8 ± 10.7; p = 0.048). In the medium PI group, SVA decreased (4.2 ± 4.6 to 3.6 ± 4.5, p = 0.020) with more posterior pelvic tilt. In the high PI group, pelvic and global posture parameters did not evolve significantly. CONCLUSION: PI is the key determining factor in pelvic tilt modification after THA. Patients with low PI demonstrate significant modification in spine, pelvic, and lower extremities. Pelvic tilt is the main adaptation mechanism for medium incidence patients whereas pelvic tilt does not change in high PI patients after surgery.

Five-year follow-up of clinical and radiological outcomes of LP-ESP elastomeric lumbar total disc replacement in active patients.

BACKGROUND CONTEXT: The surgical treatment of degenerative disc disease at the lumbar spine may involve fusion. Total disc replacement (TDR) is an alternative treatment to avoid fusion-related adverse events, specifically adjacent segment disease. New generation of elastomeric non-articulating devices has been developed to more effectively replicate the shock absorption and flexural stiffness of native disc. PURPOSE: To report 5 years clinical and radiographic outcomes, range of motion (ROM), and position of the center of rotation after a viscoelastic lumbar TDR. STUDY DESIGN: Prospective observational cohort study PATIENT SAMPLE: Sixty-one patients OUTCOME MEASURES: The clinical evaluation was based on visual analog scale (VAS) for pain, Oswestry disability index (ODI) score, short form-36 (SF-36) including the physical component summary (PCS) and the mental component summary (MCS), and general health questionnaire-28 (GHQ28). The radiological outcomes were ROM and position of the center of rotation at the index and the adjacent levels and the adjacent disc height changes. METHODS: Our study group included 61 consecutive patients with monosegmental disc replacement. We selected patients who could provide a global lumbar spine mobility analysis (intermediate functional activity according to the Baecke score). Hybrid constructs had been excluded. Only the cases with complete clinical and radiological follow-up at 3, 6, 12, 24, and 60 months were included. RESULTS: There was a significant improvement in VAS (3.3±2.5 vs. 6.6±1.7, p<.001), in ODI (20±17.9 vs. 51.2±14.6, p<.001), GHQ28 (52.6±15.5 vs. 64.2±15.6, p<.001), SF-36 PCS (58.8±4.8 vs. 32.4±3.4, p<.001), and SF-36 MCS (60.7±6 vs. 42.3±3.4, p<.001). The mean location centers of the index level and adjacent discs were comparable to those previously published in asymptomatic patients. According to the definition of Zigler and Delamarter, all of our cases remained grade 0 for adjacent level disc height (within 25% of normal). CONCLUSIONS: This series reports significant improvement in midterm follow-up after TDR, which is consistent with previously published studies but with a lower rate of revision surgery and no adjacent level disease pathologies. The radiographic assessment of the patients demonstrated the quality of functional reconstruction of the lumbar spine after LP-ESP viscoelastic disc replacement.

Are advanced three-dimensional imaging studies always needed to measure the coronal knee alignment of the lower extremity?

BACKGROUND: Coronal malalignment of the lower extremity is closely related to the onset and progression of osteoarthritis. Restoring satisfactory alignment after tibial osteotomy improves the long-term success of this conservative surgery. The purpose of our study was to determine (1) if there is a difference between two-dimensional (2D) and 3D measurements of the hip-knee-ankle (HKA) angle between the mechanical axes of the femur and the tibia, (2) which parameter most affects 2D-3D HKA measurement, and (3) the percentage of patients who are at risk of error in HKA measurement. METHODS: We reviewed imaging studies of the consecutive patients referred to us for hip or knee pain between June and October 2013. Patients with previous pelvis or lower extremity surgery were excluded. RESULTS: In 51 % (95/186) of lower extremities examined, the 3D method showed more valgus than the 2D method, and in 49 % (91/186), the 3D method showed more varus. In 12 % of extremities (23/186), the knee varus or valgus alignment was completely opposite in 3D images compared to 2D images. Having more than 7° of flexum/recurvatum alignment increased error in 2D HKA measurement by 5.7°. This was calculated to be 0.15° per 1° increase in femoral torsion and 0.05° per 1° increase in tibial torsion. Approximately 20 % of patients might be at risk of error in HKA angle measurement in 2D imaging studies. CONCLUSIONS: Orthopaedic surgeons should assess lower extremity alignment in standing position, with enough exposure of the extremity to find severe alignment or rotational deformities, and consider advanced 3D images of those patients who have them. Otherwise, HKA angle can be measured with good accuracy with 2D techniques. LEVEL OF EVIDENCE: Level-III diagnostic.

The global alignment in patients with lumbar spinal stenosis: our experience using the EOS full-body images.

Lumbar stenosis is frequently observed and treated by spine surgeons. The extent of neurological decompression and the potential spinal fixation are the basic concerns when surgery is planned. But this segmented approach to the problem is sometimes insufficient due to the complex functional situations induced by a sagittal imbalance of the patient and the combination of pathologies known as hip-spine or knee-spine syndromes. A total of 373 consecutive patients included from our EOS and clinical data base. Patients were divided in two groups. Group A included patients presenting exclusive spinal issues (172 cases) out of whom 117 (68 %) had sagittal imbalance. Among 201 patients with associated lower limbs issues (group B), 122 (61 %) had sagittal imbalance. The perception of imbalance was noticed in 54 % (93 cases) in group A and 57 % (115 cases) in group B. In the global series of 239 imbalanced cases, the key point was a spine issue for 165 patients (the 117 patients with only spine problems and 48/122 cases with combined spine and lower limbs problems). But in the patients with combined spine and lower limbs problems, we individualized hip-spine syndromes (24/122 patients) and knee-spine syndromes (13/122 patients). In some cases, (37/122 patients) the anatomical and functional situations were more complex to characterize a spine-hip or a hip-spine problem. The EOS full-body images provide new information regarding the global spinal and lower limbs alignment to improve the understanding of the patient functional posture. This study highlights the importance of the lower limb evaluation not only as compensatory mechanism of the spinal problems but also as an individualized parameter with its own influence on the global balance analysis. Level of evidence IV diagnostic case series.

The innovative viscoelastic CP ESP cervical disk prosthesis with six degrees of freedom: biomechanical concepts, development program and preliminary clinical experience.

The viscoelastic cervical disk prosthesis ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP ESP lumbar disk implanted since 2006. CP ESP provides six full degrees of freedom about the three axes including shock absorbtion. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. The concept of the ESP prosthesis is fundamentally different from that of the devices currently used in the cervical spine. The originality of the concept of the ESP® prosthesis led to innovative and intense testing to validate the adhesion of the viscoelastic component of the disk on the titanium endplates and to assess the mechanical properties of the PCU cushion. The preliminary clinical and radiological results with 2-year follow-up are encouraging for pain, function and kinematic behavior (range of motion and evolution of the mean centers of rotation). In this series, we did not observe device-related specific complications, misalignment, instability or ossifications. Additional studies and longer patient follow-up are needed to assess long-term reliability of this innovative implant.

Offset and anteversion reconstruction after cemented and uncemented total hip arthroplasty: an evaluation with the low-dose EOS system comparing two- and three-dimensional imaging.

PURPOSE: Accurate evaluation of femoral offset is difficult with conventional anteroposterior (AP) X-rays. The EOS imaging system is a system that makes the acquisition of simultaneous and orthogonal AP and lateral images of the patient in the standing position possible. These two-dimensional (2D) images are equivalent to standard plane X-rays. Three-dimensional (3D) reconstructions are obtained from these paired images according to a validated protocol. This prospective study explores the value of the EOS imaging system for comparing measurements of femoral offset from these 2D images and the 3D reconstructions. METHODS: We included 110 patients with unilateral total hip arthroplasty (THA). The 2D offset was measured on the AP view with the same protocol as for standard X-rays. The 3D offset was calculated from the reconstructions based on the orthogonal AP and lateral views. Reproducibility and repeatability studies were conducted for each measurement. We compared the 2D and 3D offset for both hips (with and without THA). RESULTS: For the global series (110 hips with and 110 without THA), 2D offset was 40 mm (SD 7.3; 7-57 mm). The standard deviation was 6.5 mm for repeatability and 7.5 mm for reproducibility. Three-dimensional offset was 43 mm (SD 6.6; 22-62 mm), with a standard deviation of 4.6 for repeatability and 5.5 for reproducibility. Two-dimensional offset for the hips without THA was 40 mm (SD 7.0; 26-56 mm), and 3D offset 43 mm (SD 6.6; 28-62 mm). For THA side, 2D offset was 41 mm (SD 8.2; 7-57 mm) and 3D offset 45 mm (SD 4.8; 22-61 mm). Comparison of the two protocols shows a significant difference between the 2D and 3D measurements, with the 3D offset having higher values. Comparison of the side with and without surgery for each case showed a 5-mm deficit for the offset in 35 % of the patients according to the 2D measurement but in only 26 % according to the 3D calculation. CONCLUSIONS: This study points out the limitations of 2D measurements of femoral offset on standard plane X-rays. The reliability of the EOS 3D models has been previously demonstrated with CT scan reconstructions as a reference. The EOS imaging system could be an option for obtaining accurate and reliable offset measurements while significantly limiting the patient's exposure to radiation.

Clinical outcomes, radiologic kinematics, and effects on sagittal balance of the 6 df LP-ESP lumbar disc prosthesis.

BACKGROUND CONTEXT: Surgical treatment of degenerative disc disease remains a controversial subject. Lumbar fusion has been associated with a potential risk of segmental junctional disease and sagittal balance misalignment. Motion preservation devices have been developed as an alternative to fusion. The LP-ESP disc is a one-piece deformable device achieving 6 df, including shock absorption and elastic return. This is the first clinical report on its use. PURPOSE: To assess clinical outcomes and radiologic kinematics in the first 2 years after implantation. STUDY DESIGN: Prospective cohort of patients with LP-ESP total disc replacement (TDR) at the lumbar spine. PATIENT SAMPLE: Forty-six consecutive patients. OUTCOME MEASURES: Clinical outcomes were the visual analog scale (VAS) for pain, the Oswestry disability index (ODI), and the GHQ28 (General Health Questionnaire) psychological score. Radiologic data were the range of motion (ROM), sagittal balance parameters, and mean center of rotation (MCR). METHODS: Patients had single-level TDR at L4-L5 or L5-S1. Outcomes were prospectively recorded for 2 years (before and at 3, 6, 12, and 24 months after surgery). The SpineView software was used for computed analysis of the radiographic data. Paired t tests were used for statistical comparisons. RESULTS: No intraoperative complication occurred. All clinical scores improved significantly at 24 months: the back pain VAS scores by a mean of 4.1 points and the ODI by 33 points. The average ROM of the instrumented level was 5.4°±4.8° at 2 years and more than 2° for 76% of prostheses. The MCR was in a physiological area in 73% of cases. The sagittal balance (pelvic tilt, sacral slope, and segmental lordosis) did not change significantly at any point of the follow-up. CONCLUSIONS: Results from the 2-year follow-up indicate that LP-ESP prosthesis recreates lumbar spine function similar to that of the healthy disc in terms of ROM, quality of movement, effect on sagittal balance, and absence of modification in the kinematics of the upper adjacent level.

Assessment of the axial rotation of the pelvis with the EOS® imaging system: intra- and inter-observer reproducibility and accuracy study.

PURPOSE: A source of radiological bias occurs when the axial rotation of the pelvis is disregarded in hip and spine biomechanics analyses. The EOS imaging system (EOS Imaging, France) offers the possibility of detecting and measuring the axial rotation of bones. Reproducibility and accuracy have not been documented in the case of the pelvis. METHODS: A dry pelvis has been X-rayed with the EOS system every 5° from 30° left to 30° right according to a laser line reference goniometer. Three observers have measured the rotation. One observer did it 3 times. The intra- and inter-observer reproducibility and the accuracy have been calculated using the root mean square standard deviation calculation. The relationship between the axial rotation and the offset between the left and right acetabulae on the lateral view was investigated. RESULTS: The 95 % CI was ±0.23° for the intra-observer and ±0.33° for the inter-observer reliability. The mean of signed differences between the software calculation and the actual axial rotation of the pelvis was -0.39° (SD 0.77°). The lateral acetabular offset was proportional to the sin of the rotation. Approximately, 30 mm offset corresponded to about 10° rotation. CONCLUSIONS: The 3D slot scanning imaging system demonstrated significant reproducibility and accuracy for the assessment of the axial rotation of the pelvis.

Risk of impingement and third-body abrasion with 28-mm metal-on-metal bearings.

BACKGROUND: Concerns have been raised about the sequelae of metal-on-metal (MoM) bearings in total hip arthroplasty (THA). However, retrieval studies, which offer the best insight into the clinically relevant mechanisms of MoM wear, have followed predictable trends to date such as indicting cobalt-chromium (CoCr) metallurgy, cup design, high conformity between the head and cup, "steep cups," "microseparation," and "edge wear." QUESTIONS/PURPOSES: We wished to evaluate a set of retrieved 28-mm MoM THA for signs of (1) cup-to-stem impingement; (2) normal wear pattern and concomitant stripe damage on femoral heads that would signify adverse wear mechanics; and (3) well-defined evidence of third-body scratches on bearings that would indicate large abrasive particles had circulated the joint space. METHODS: Ten 28-mm MOM retrievals were selected on the basis that femoral stems were included. Revision surgeries at 3 to 8 years were for pain, osteolysis, and cup loosening. CoCr stems and the MoM bearings were produced by one vendor and Ti6Al4V stems by a second vendor. All but two cases had been fixed with bone cement. We looked for patterns of normal wear and impingement signs on femoral necks and cup rims. We looked for adverse wear defined as stripe damage that was visually apparent on each bearing. Wear patterns were examined microscopically to determine the nature of abrasions and signs of metal transfer. Graphical models recreated femoral neck and cup designs to precisely correlate impingement sites on femoral necks to cup positions and head stripe patterns. RESULTS: The evidence revealed that all CoCr cup liners had impinged on either anterior or posterior facets of femoral necks. Liner impingement at the most proximal neck notch occurred with the head well located and impingement at the distal notch occurred with the head rotated 5 mm out of the cup. The hip gained 20° motion by such a subluxation maneuver with this THA design. All heads had stripe wear, the basal and polar stripes coinciding with cup impingement sites. Analysis of stripe damage revealed 40 to 100-µm wide scratches created by large particles ploughing across bearing surfaces. The association of stripe wear with evidence of neck notching implicated impingement as the root cause, the outcome being the aggressive third-body wear. CONCLUSIONS: We found consistent evidence of impingement, abnormal stripe damage, and evidence of third-body abrasive wear in a small sample of one type of 28-mm MoM design. Impingement models demonstrated that 28-mm heads could lever 20° out of the liners. Although other studies continue to show good success with 28-mm MoM bearings, their use has been discontinued at La Pitie Hospital.

The LP-ESP(®) lumbar disc prosthesis with 6 degrees of freedom: development and 7 years of clinical experience.

The viscoelastic lumbar disk prosthesis-elastic spine pad (LP-ESP(®)) is an innovative one-piece deformable but cohesive interbody spacer providing 6 full degrees of freedom about the 3 axes, including shock absorption. A 20-year research program has demonstrated that this concept provides mechanical properties very close to those of a natural disk. Improvements in technology have made it possible to solve the problem of the bond between the elastic component and the titanium endplates and to obtain an excellent biostability. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. It thus differs substantially from current prostheses, which are 2- or 3-piece devices involving 1 or 2 bearing surfaces and providing 3 or 5 degrees of freedom. This design and the adhesion-molding technology differentiate the LP-ESP prosthesis from other mono-elastomeric prostheses, for which the constraints of shearing during rotations or movement are absorbed at the endplate interface. Seven years after the first implantation, we can document in a solid and detailed fashion the course of clinical outcomes and the radiological postural and kinematic behavior of this prosthesis.

Sacropelvic fixation with iliosacral screws: applications and results in adult spinal deformities.

STUDY DESIGN: Retrospective radiographic and clinical review. OBJECTIVE: To determine the feasibility of iliosacral screw fixation in adult spinal deformations. SUMMARY OF BACKGROUND DATA: Pelvic fixation is one of the most challenging instrumentation problems. The poor bone quality frequently found within the sacrum and the large lumbosacral loads with cantilever pullout forces across this region explain its frequent failure. METHODS: Fourteen adult patients undergoing pelvic fixation using iliosacral screws with a minimal follow-up of 24 months were analyzed for radiographic outcomes. Radiographic data included the localization of the spinal deformity, the Cobb angle, T4-T12 thoracic kyphosis, L1-S1 lumbar lordosis, the T9 tilt, the pelvic parameters, and the POA. Mechanical and infectious complications were also noted. RESULTS: The lumbo-pelvic correction was performed with a large reduction of the POA in every case. The frontal and sagittal corrections obtained with this procedure were considered as being effective. There were no mechanical complications due to failure of the instrumentation, loss of sacral fixation, or loss of lumbar lordosis at the time of the last follow-up. One patient experienced local infection on the left iliosacral screw without any residual functional sequel. DISCUSSION: Iliosacral screwing can offer a pelvic fixation reliable enough to allow restoration of 3-dimensional trunk balance. This technique has a quite short learning curve and adequately permits frontal and sagittal corrections, increases stability, and decreases instrumentation-related complications. Our observations suggest that it is applicable to pelvic fixation in adult surgery.

Preoperative evaluation of the cervical spondylotic myelopathy with flexion-extension magnetic resonance imaging: about a prospective study of fifty patients.

STUDY DESIGN: The authors evaluated preoperative modifications of the cervical spinal canal in flexion and extension in 50 patients with cervical spondylotic myelopathy (CSM) and looked for impingement of the spinal cord not diagnosed in the neutral position. OBJECTIVE: To evaluate the usefulness of preoperative flexion-extension magnetic resonance imaging (MRI) for patients with CSM. SUMMARY OF BACKGROUND DATA: Dynamic factors contribute to CSM. Although the clinical manifestations and spinal or spinal cord morphology in patients with myelopathy have been reported, to our knowledge, there are no studies that include the cervical spinal cord length, sagittal diameter, and available space in patients with CSM in flexion, extension, and the neutral position. METHODS: Dynamic MRI changes in canal stenosis during flexion-extension were evaluated in 50 patients with CSM in the supine position. The authors determined length of the cervical cord (LCC, C1-C7), cervical cord sagittal diameter (CCSD, C3-T1), cervical cord available space (CCAS, C3-T1), intramedullary high-intensity signal (IHIS) changes, number of stenosis, and severity of cord impingement in flexion, extension, and the neutral positions. RESULTS: On both the anterior and posterior edges of the cord, mean LCC in flexion was longer than in extension or the neutral position and longer in the neutral position than in extension (P < 0.05). In all three positions, the average length of the anterior edge of the cervical cord was longer than the posterior edge (P < 0.05). The mean value of CCSD at each level in extension was greater than in flexion or the neutral position (P < 0.05). In the neutral position, CCSDs were greater than in flexion from C4 to C7 (P < 0.05), but this difference failed to reach significance at levels C3 and T1. In the neutral position, CCAS was greater than in either extension or flexion (P < 0.05), and CCAS was greater in flexion than in extension (P < 0.05) at all levels except C6, at which CCAS was greater in flexion than in either extension or the neutral position (P < 0.05). MRI demonstrated functional cord impingement (grade 3 of Mühle) in 6 of the 50 (12%) patients in flexion, in 17 patients (34%) in the neutral position, and in 37 patients (74%) in extension. IHIS was observed in flexion in 20 patients (40%), in the neutral position in 13 patients (26%), and in extension in 7 patients (14%). CONCLUSION: Cervical spondylotic myelopathy results from the synergistic action of static and dynamic factors, the latter of which play an important role. In some patients, IHIS on T2 images is only visible with the neck in flexion. That might explain why IHIS is first detected after surgery in some patients in whom MRI was obtained before surgery only in the neutral position. Dynamic MRI is useful to determine more accurately the number of levels where the spinal cord is compromised, and to better evaluate narrowing of the canal and IHIS. New information provided by flexion-extension MRI might change our strategy for CSM management.

Acetabular anteversion with CT in supine, simulated standing, and sitting positions in a THA patient population.

BACKGROUND: Appraisal of the orientation of implants in THA dislocations currently is based on imaging done with the patient in the supine position. However, dislocation occurs in standing or sitting positions. Whether measured anteversion differs in images projected in the position of dislocation is unclear. QUESTIONS/PURPOSES: We compared measured acetabular cup orientations on axial CT scans taken with the patient in a supine position with those from CT sections at angles to the sacral slope reflecting standing and sitting positions. METHODS: We retrospectively reviewed the radiographs of 328 asymptomatic patients who had THAs. Anatomic acetabular anteversion (AAA) was measured from the plain CT scan (supine position, axial CT sections). The AAA also was measured on reformatted CT scans in which the orientation was adjusted individually to the sacral slope on lateral radiographs with patients in the standing and sitting positions. RESULTS: The mean/(SD) AAA changed from 24.2° (6.9°) in the supine position to 31.7° (5.6°) and 38.8° (5.4°) in simulated standing and sitting positions, respectively. The supine AAA correlated with the standing AAA (r = 0.857) but not with the sitting AAA (r = 0.484). CONCLUSIONS: These data suggest measurement of the AAA on a plain CT scan used in current practice is biased. In patients with recurrent posterior dislocation from a sitting position, accounting for the functional variations in measurement of the position of the acetabular cup provides more relevant information regarding component positioning.

Shortening osteotomy and sacro-sacral fixation for U-shaped sacral fractures.

STUDY DESIGN: Technical note and retrospective first cases study. OBJECTIVE: To present a novel surgical procedure for treating rare and challenging U-shaped fractures of the sacrum. SUMMARY OF BACKGROUND DATA: U-shaped fractures of the sacrum are not frequent and usually seen in the context of high energy trauma (high-fall injury). There is no consensus about the therapeutic strategy. When surgery is decided on selected patients, the technique raises several issues for the neural decompression, reduction, and fixation. The L5-S1 mobility has to be sacrificed for most authors. METHODS: Based on anatomic considerations, the authors present here the original surgical technique they have been using at their institution and a consecutive series of patients. The procedure associates a shortening osteotomy of the sacrum at the site of the fracture and a sacro-sacral fixation. RESULTS: The proposed procedure was simple, safe, and effective. CONCLUSIONS: Performing the osteotomy helps in the reduction and allows a short fixation, which spares the mobility of the lumbo-sacral junction.

Modification of pelvic orientation after total hip replacement in primary osteoarthritis.

The acetabular anteversion angle varies according to the position of the pelvis. The objective goal of our study was to investigate changes in pelvic orientation after total hip replacement for primary osteoarthritis. We studied 89 patients who underwent total hip replacement for primary unilateral osteoarthritis. Lateral pelvic X-rays that included the hips were performed pre-operatively and one year post-operatively. Reference values were calculated by carrying out the same analysis in 100 asymptomatic healthy volunteers. Pelvic orientation was analyzed using the sacral slope. Patients having surgery for osteoarthritis had a decreased pelvic range of motion pre-operatively and post-operatively when compared to healthy volunteers. Post-operatively, this range of motion increased by 3 degrees but remained lower than the norm. Compared to asymptomatic healthy volunteers, patients affected by osteoarthritis had a posterior pelvic extension that decreased post-operatively but did not return to norm. This post-operative pelvic inclination generates a significant decrease in the final cup anteversion and thus may predispose to posterior dislocation. As this post-operative alteration to pelvic orientation cannot be anticipated, computer-aided surgery for cup positioning may not improve the accuracy of the acetabular anteversion in some patients.